Commutators for electric machines



'June 27, 1961 F. scHAFER 2,990,489

COMMUTATORS FOR ELECTRIC MACHINES Filed Sept. 8, 1958 Fig.1

26a 37 n Fig-3 as N 3,, I. W .99 30a I I 29a 32 mll ,m

United States Patent 2,990,489 COMMUTATORS FOR ELECTRIC MACHINES Fridolin Schiifer, Stuttgart, Germany, assignor to Firma Robert Bosch G.m.b.H., Stuttgart, Germany Filed Sept. 8, 1958, Ser. No. 759,696 Claims priority, application Germany Oct. 19, 1957 6 Claims. (Cl. 310-435) The present invention relates to commutators for electric machines, especially small electric machines, and more particularly to improvements in commutators of the type in which the annulus consisting of dovetailed insulated segments is held together by a pair of clamping rings and by a tubular core or rivet whose ends are deformed or swedged to bear against the end faces of clamping rings and to thereby hold the segments in proper position with respect to the axis about which the commutator revolves.

According to the invention disclosed in a copending application of Karl Wick, Serial No. 759,695, now abandoned, displacements of dovetailed segments in commutators having a rivet like core are prevented by introducing a hardenable plastic insulating substance into the space defined by the exposed surfaces of dovetailed portions and the peripheral zone of the core or rivet which latter, as above stated, urges a pair of clamping rings against the annulus of insulated segments and thus constitutes the locking means for all component parts. According to said invention, the insulating substance is introduced through at least one aperture which constitutes a communicating passage between said space and the axial bore of the commutators core. The apparatus for introducing the insulating substance, preferably a material of good heat conductivity such as Bakelite or another synthetic product, comprises a pair of rams extending into the axial bore of the core, the rams compressing the insulating substance therebetween sufiiciently to transform the latter into a plastic mass which enters the space between dovetailed portions of the segments and the core through the aforementioned aperture or apertures and fills the space to prevent, after hardening thereof, any tilting of segments about the clamping rings. The tilting of segments is undesirable as it would cause rapid destruction of the runway (ie the peripheral zone of the annulus of segments) which is in contact with customary carbon brushes or wipers when the commutator is put to use. Since the insulating substance is introduced into the annulus of segments through the core, the step must be performed before the commutator is mounted onto the spindle of an armature because the spindle, too, passes through the axial bore of said core.

An object of the present invention is to provide a commutator of the above described characteristics which is so constructed that the insulating material may be introduced into the space between dovetailed portions of segments and the peripheral zone of the core while the commutator is already mounted on the spindle of an armature, that is, after the armature wires are already soldered to the segments of the commutator.

Another object of the invention is to provide a commutator of the type above set forth which is so constructed that the insulating substance which prevents tilting of segments about their clamping rings may be introduced simultaneously with the step of coating the armature coil with the same insulating substance, i.e. that the coating of armature coil and the filling of annulus with a view to prevent tilting of segments may be performed simultaneously.

The above and certain other objects of the invention are attained by the provision of a commutator in which at least one clamping ring is formed with one or more bores and/or grooves constituting channels or communi- 2,990,489 Patented June 27, 1961 cating passages between the surrounding atmosphere and the space defined by dovetailed portions of segments and by the peripheral zone of the commutators core, whereby the insulating material need not be introduced through the axial bore in the core. Accordingly, the introduction of insulating material into the aforementioned space need not precede the step of mounting the commutator on the spindle of an armature as the material may be introduced at any time due to accessibility of one end of each channel in the clamping rings regardless of whether the axial bore in the core is filled or not.

It is preferred to provide at least three channels in each clamping ring and to angularly space the channels from each other. The channels in clamping rings may consist of bores perpendicular or inclined with respect to the axis of a commutator, or each channel may consist of an arcuate groove and an axially parallel groove, the latter having one of its ends in communication with the space between the annulus of segments and the core of the commutator.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of three specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is an axial section through approximately onehalf of a commutator constructed in accordance with my invention wherein the bores in clamping rings are inclined with respect to the axis about which the commutator rotates;

FIG. 2 is a similar section through a commutator whose clamping rings are provided with radial bores perpendicular to the axis of rotation; and

FIG. 3 is a similar sectional view of a commutator in which the channels in clamping rings consist of arcuate and axially parallel grooves,

Referring now in greater detail to FIG. 1, the commutator therein shown comprises an annulus of wedgeshaped segments 11 insulated from each other by interposed layers or sheets 12 of non-conducting material, e.g. mica; a pair of clamping rings 14, 15 so shaped as to extend into the axial bore of annulus and into the V-shaped annular recesses defined by dovetailed portions 13 of segments 11; a pair of insulating rings 17, 18 which prevent short-circuiting of segments 11 by clamping rings 14, 15; and a cylindrical core or rivet 16 whose ends 16a, 16]) are bent over or swedged and extend into the recesses provided in the end faces 14a, 15a of respective clamping rings. Surfaces 13a on dovetailed portions 13 and similar surfaces on the dovetailed portions of non-conducting intermediate members 12 define with the peripheral zone Me of core 16 an annular space 19 which communicates with bores or channels 20 and 21 in respective clamping rings 14, 15. As shown, there are annular clearances 17a, 1&1 between inserts 17, 18 and the periphery 16c of the core. Bores or channels 20, 21 are inclined with respect to the longitudinal axis of the commutator and terminate in the peripheral surfaces 14b, 15b of respective clamping rings. To that end, rings 14, 15 extend somewhat beyond the longitudinal ends of annular body constituted by members 11 and 12. Thus, the peripheral zones of rings 14, 15 are partly received in the axial bore of annulus consisting of members 11, 13 and extend partly beyond the adjacent ends of the annulus. Outer ends of channels 20, 21 terminate in the peripheral zones of respective rings 14, 15 beyond the adjacent ends of the annulus,

Core 16 has an axial bore 164 which receives the spindle of an armature (not shown) when the commutator is put to use. It will be readily understood that, since the hardenable insulating material 40 (shown in FIG. 2) may be introduced in plastic state through bores or channels '20, 21 in clamping ring 14 or 15, the filling of annular space 19 with such substance may occur before or after the segments are soldered to the wires of an armature. It is preferred to provide at least three spaced bores in each clamping ring.

Insulating material 40 is of such characteristics that it will become plastic under suficient pressure and will harden in the annular space 19. While the plastic material is introduced through the bores in one clamping ring, air is free to escape from space 19 through the bores in the other clamping ring. The purpose of hardenable substance 40 is to prevent the tilting of segments 11 about inwardly extending V-shaped portions of clamping rings 14, which could upset the arrangement of segments with respect to the axis of a commutator and would rapidly destroy the latter after relatively short periods of use. The substance 40, after hardening, counteracts radially inwardly directed components of force which acts between rings 14, 15 and the dovetailed portions 13 of commutator segments 11. Axial movements of annulus consisting of members 11, 12 are prevented by the deformed end portions 16a, 16b of core M which act against the end faces 14a, 15a of rings 14, 15. Any radial movements of segments 11 and of non-conducting members 12 are prevented by the hardened insulating body 40 on the one hand, and by the V-shaped inwardly facing extensions of clamping rings 14, 15 on the other hand. Thus, segments 11 and members 12 are prevented from any movements with respect to the commutator axis and maintain their truly radial position.

The provision of bores or channels in both clamping rings is particularly important if the insulating material in space 19 is an epoxy resin or if said space is filled by immersing the commutator in vacuo into a suitable hardenable insulating plastic material.

Referring now to FIG. 2, the construction of members 11, 12 and 16 is identical with those shown in FIG. 1. Insulating inserts 22, 23 are slightly modified in that they extend only between the inclined surfaces of dovetailed portions 13 and of respective clamping rings 26, 27. Bores or channels 24, 25 in rings 26, 2.7, respectively, are radial, is. perpendicular to the axis of core 16, and communicate with the annular space 19 through clearances 26a, 27a between respective members 26, 27 and the peripheral zone 160 of core 16. Instead of providing clearances 26a, 27a between the clamping rings and the core 16, members 26, 27 are preferably provided with suitable axially parallel grooves in the walls surrounding their axial bores through which the insulating material 40 may pass from respective bores 24, 25 into the space 19. In this embodiment, too, outer ends of bores or channels 24, 25 terminate at the peripheral zones 26b, 27b of the clamping rings and beyond the ends of members 11, 12 to permit introduction of hardenable insulating material regardless of whether or not the spindle of an armature passes through the axial bore 16a of the commutators core 16.

The embodiment of my invention shown in FIG. 3 differs from that illustrated in FIG. 2 only in the construction of clamping rings 29, 30. Arcuate grooves 31, 32 in respective members '29, terminate at the latters end faces 29a, 30a. In addition, there are provided axially parallel cutouts or grooves 34, in respective members 29, 30, these cutouts constituting communicating passages between the inner terminals of arcuate grooves or bores 31, 32 and the annular space 19. As shown, grooves 34, 35 are formed by removing layers of material from the walls surrounding the axial openings of clamping rings 29, 30, respectively. Insulating inserts 36, 37 correspond to and serve the same purposes as members 22, 23 shown in FIG. 2. Grooves 31, 34 and 32, 35 constitute channels communicating with space 19 at one end and with surrounding atmosphere at the other end.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A commutator comprising, in combination; an an.- nulus of insulated segments having two ends, an axis, and a coaxial bore, each segment having a dovetailed portion extending toward said bore and each dovetailed portion having a surface turned toward the axis of said annulus; a core coaxially received in said bore, said core having a pair of deformed end portions and a peripheral Zone defining an annular space with the surfaces of said dovetailed portions; a pair of clamping rings, one at each end of said annulus, each ring having an end face engaged by one end portion of said core, a V-shaped extension engaging with said dovetailed portions in such manner as to urge said segments toward the axis of said annulus, and an axial opening surrounding the peripheral zone of said core, at least one of said rings defining at least one channel having one terminal in communication with said space and another terminal in the end face of the respective ring, each channel comprising a first groove having one end terminating in the end face and another end communicating with the opening of the respective ring, and a second groove having one end communicating with the last mentioned end of said first groove and another end communicating with said space; and a hardenable insulating substance filling said space.

2. A commutator comprising, in combination: an anulus of insulated segments having two ends, an axis, and a coaxial bore, each segment having a dovetailed portion extending toward said bore and each dovetailed portion having a surface turned toward the axis of said annulus; a core coaxially received in said bore, said core having a pair of deformed end portions and a peripheral zone defining an annular space with the surfaces of said dovetailed portions; a pair of clamping rings, one at each end of said annulus, each ring having an end face engaged by one end portion of said core, a V-shaped extension engaging with said dovetailed portions in such manner as to urge said segments toward the axis of said annulus, and an axial opening surrounding the peripheral zone of said core, each ring defining at least one channel having one terminal in communication with said space and another terminal in the end face of the respective ring, each channel comprising a first groove having one end terminating in the end face and another end communicating with the opening of the respective ring, and a second groove having one end communicating with the last mentioned end of said first groove and another end communicating with said space; and a hardenable insulating substance filling said space.

3. A commutator comprising, in combination: an annulus of insulated segments having two ends, an axis, and a coaxial bore, each segment having a dovetailed portion extending toward said bore and each dovetailed portion having a surface turned toward the axis of said annulus; a core coaxially received in said bore, said core having a pair of deformed end portions and a peripheral zone defining an annular space with the surfaces of said dovetailed portions; a pair of clamping rings, one at each end of said annulus, each ring having an end face engaged by one end portion of said core, a V-shaped extension engaging with said dovetailed portions in such manner as to urge said segments toward the axis of said annulus, and an axial opening surrounding the peripheral zone of said core, at least one of said rings defining at least one channel having one terminal in communication with said space and another terminal in the end face of the respective ring, each channel comprising a first groove having one end terminating in the end face and another end communicating with the opening of the respective ring, and a second groove parallel with the axis of said annulus and formed in the material of the respective ring surrounding said opening, said second groove having one end communicating with the last' mentioned end of said first groove and another end communicating with said space; and a hardenable insulating substance filling said space.

4. A commutator comprising, in combination, an annulus of insulated segments having two ends, an axis, and a coaxial bore, each segment having a dovetailed portion extending toward said bore and each dovetailed portion having a surface turned toward the axis of said annulus; a core coaxially received in said bore, said core having a pair of deformed end portions and a peripheral zone defining an annular space with said surfaces of said dovetailed portions; a pair of clamping rings, one at each end of said annulus, each ring having an end face engaged by one end portion of said bore, a V-shaped extension 6 engaging with said dovetailed portions in such a manner as to urge said segments toward the axis of said annulus, and an axial opening surrounding the peripheral zone of said bore, each clamping ring defining at least one channel having one end communicating with the surrounding atmosphere and another end communicating with said space; and a hardenable insulating material in said space.

5. A commutator as defined in claim 4 in which each of said channels is formed by a bore through the respective clamping ring and extending inclined to the axis of said annulus.

6. An arrangement as defined in claim 4 in which each of said channels is formed by a radial bore through the respective clamping ring and extending at substantially right angle to the axis of said annulus.

References Cited in the file of this patent UNITED STATES PATENTS 1,354,005 Sloan Sept. 28, 1920 1,503,484 Conklin Aug. 5, 1924 1,845,114 Apple Feb. 16, 1932 2,677,874 Nichols May 11, 1954 2,721,283 Kurath Oct. 18, 1955 

